1. Field of the Invention
The present invention relates to a plastic molded semiconductor package and a method of manufacturing the same, and in particular, relates to a structure of a CSP (Chip Scale Package) and a method of manufacturing the same.
2. Description of the Related Art
In recent years, a demand for high-density mounting of packages in semiconductor devices has been increased. In accordance with this, the reduction of package size has been demanded. Various technologies, therefore, have been developed for reducing the size of packages. An example of the technology for reducing the package size is disclosed in Japanese Patent Laying-Open No. 2-49460 (1990). A plastic molded semiconductor package disclosed in this Japanese Patent Laying-Open No. 2-49460 will be described below.
FIG. 44 is a cross section showing the plastic molded semiconductor package disclosed in the Japanese Patent Laying-Open No. 2-49460. Referring to FIG. 44, a semiconductor chip 101 is provided at its main surface with pad electrodes 102, each of which functions as a part of an electrode for external extension (i.e., an electrode for external connection). A passivation film 103, which partially exposes a surface of each pad electrode 102, is formed on the main surface of the semiconductor chip 101. In this specification, the electrode for extension (i.e., electrode for external connection) is defined as an electrode used for electrical connection between elements in the semiconductor chip 101 and an electrode of an external equipment.
The pad electrode 102 is provided at its surface portion with a protruded electrode 104. The semiconductor chip 101 is molded with a molding resin 105, which partially exposes a surface of each protruded electrode 104.
Owing to the above structures, the plastic molded semiconductor package 100 can have the size nearly equal to those of the semiconductor chip 101. In other words, the sizes of plastic molded semiconductor package can be reduced. Consequently, the plastic molded semiconductor package suitable to high-density mounting can be obtained.
Following contents have been disclosed as a method of manufacturing the plastic molded semiconductor package 100 having the above structures. The protruded electrode 104 is formed by a well-known thick-film printing method. The resin encapsulation is carried out by a potting method or a transfer mold method.
The plastic molded semiconductor package 100 thus constructed, however, suffers from following problems, which will be described below with reference to FIGS. 45 to 50.
Referring to FIG. 45, a first problem of the conventional plastic molded semiconductor package 100 will be described below. FIG. 45 is a fragmentary enlarged cross section showing the first problem of the conventional plastic molded semiconductor package 100.
The protruded electrode 104 and the molding resin 105 are made of different materials, and thus have different coefficients of thermal expansion. Referring to FIG. 45, the protruded electrode 104 and the molding resin 105 are in contact with each other through a short length L and hence through a relatively small area. Therefore, when heat is applied to the protruded electrode 104, for example, in an operation for joining the plastic molded semiconductor package 100 on a printed board, the interfaces of the molding resin 105 and protruded electrode 104 are liable to delaminate due to expansion of the protruded electrode 104.
As a result, as shown in FIG. 45, a space 106 is liable to generate between the interfaces of the protruded electrode 104 and seal resin 105. This results in a problem that moisture resistance of the plastic molded semiconductor package 100 is deteriorated.
Referring to FIG. 46, a second problem of the conventional plastic molded semiconductor package 100 will be described below. FIG. 46 is a cross section showing an operation for mounting the conventional plastic molded semiconductor package 100 on a printed board 107.
Referring to FIG. 46, the printed board 107 is provided at its surface with electrodes 108 for electrical connection with the protruded electrodes 104. Each electrode 108 is provided at its surface with a joining member such as soldering paste for joining the electrode 108 and protruded electrode 104 together.
In the conventional plastic molded semiconductor package 100, a portion of the protruded electrode 104 located in the molding resin 105 has a diameter substantially equal to that of a portion thereof protruded externally from the seal resin 105. Thus, the portion of the protruded electrode 104 protruded from the seal resin 105 has a relatively small surface area.
This results in a problem that only a small margin is ensured for the positioning of the printed board 107 and plastic molded semiconductor package 100 when mounting the package 100 on the printed board 107. Also, the protruded electrode 104 is liable to fall from the surface of the electrode 108 on the printed board 107 when mounting the package 100 on the printed board 107, resulting in joining failure.
Referring to FIGS. 47 and 48, a third problem of the conventional plastic molded semiconductor package 100 will be described below. FIG. 47 is a cross section showing the plastic molded semiconductor package 100 suffering from the third problem. FIG. 48 is a plan showing an operation for mounting the plastic molded semiconductor packages 100 shown in FIG. 47 on the printed board 107.
Referring first to FIG. 47, it is difficult to hold the semiconductor chip 101 at a predetermined position during the resin encapsulation in a conventional method of manufacturing the plastic molded semiconductor package 100. No prior art has disclosed a method for holding the semiconductor chip 101 at the predetermined position. Therefore, the semiconductor chip 101 is deviated from the predetermined position in the molding resin 105 in some cases as shown in FIG. 47.
Therefore, the protruded electrodes 104 are protruded at positions deviated from the surface of the molding resin 105. More specifically, one of the protruded electrodes 104 is spaced by a distance L2 from the side of the package 100, while the other protruded electrode 104 is spaced from the side of the package 100 by a distance L1 longer than the distance L2 in some cases.
This results in a problem that the electrodes cannot be uniformly positioned in the plastic molded semiconductor package, and thus alignment in the mounting operation is difficult. Even if the plastic molded semiconductor package 100 is mounted on the printed board, a following problem may generate.
Referring to FIG. 48, four plastic molded semiconductor packages 100a, 100b, 100c and 100d are mounted on the surface of the printed board 107. These four plastic molded semiconductor packages 100a, 100b, 100c and 100d are mounted at shifted positions on the printed board 107 because they are provided with the protruded electrodes 104 located at different positions. This is disadvantageous in view of the high-density mounting of the plastic molded semiconductor packages 100 on the printed board 107.
Referring to FIGS. 49A and 49B, a fourth problem of the conventional plastic molded semiconductor package 100 will be described below. FIG. 49A is a cross section showing the conventional plastic molded semiconductor package 100 suffering from the fourth problem. FIG. 49B is a fragmentary enlarged cross section showing a region A in FIG. 49A.
Referring to FIGS. 49A and 49B, a mold flash 105a of resin is liable to leave around the surface of the protruded electrode 104 not to be covered with the molding resin 105 according to the method of resin encapsulation of the conventional plastic molded semiconductor package 100. This is due to the fact that it is difficult to hold the protruded electrode 104 or semiconductor chip 101 so as to prevent the flow of resin into the vicinity of the tip end of protruded electrode 104 when encapsulating.
If the plastic molded semiconductor package 100 including the mold flash 105a around the protruded electrode 104 were mounted on the printed board, a following problem would generate. Thus, electrical connection failure may generate between the protruded electrode 104 and an electrode formed on the printed board.
Even if the electric connection is formed, a fillet (meniscus), which is formed of a joining member 109 for joining the electrode 104 to the electrode on the printed board, is not formed around the protruded electrode 104, because the mold flash 105a is formed around the protruded electrode 104. This results in a problem that a mechanical joining strength between the protruded electrode 104 and the printed board remarkably decreases.
Therefore, it may be desirable to remove the mold flash 105a by an appropriate method. Removal of the mold flash 105a, however, applies damage against the protruded electrode 104 and/or a portion around the same, so that the reliability is liable to be impaired.
Then, a fifth problem of the conventional plastic molded semiconductor package 100 will be described below. FIG. 50A is a cross section showing the conventional plastic molded semiconductor package 100 suffering from the fifth problem. FIG. 50B is a cross section showing an example of the structures in which the semiconductor chip 101 including protruded electrodes 104a and 104b of different heights is encapsulated with the molding resin 105.
Referring to FIG. 50A, the protruded electrode 104 is formed by the thick-film printing in the prior art. Therefore, there is deviation in the supply amounts of material for forming the protruded electrodes 104. If the protruded electrodes 104 of relatively large heights are to be formed, as is done in the prior art, the deviation in the supply amounts of material of the protruded electrodes 104 is reflected on the difference in the heights of the protruded electrodes 104. In the extreme case, one of the protruded electrodes 104a is protruded from the seal resin 105 through a height L3, while the other protruded electrode 104b is protruded from the surface of the seal resin through a height L4 longer than the height L3 as shown in FIG. 50A. This results in the difficulty in the mounting operation of the plastic molded semiconductor package on the printed board.
A following problem may also be caused by encapsulating the semiconductor chip 101 having the protruded electrodes 104a and 104b of different heights with the molding resin 105. In an example of resin encapsulation, a die 110 which has concavities 110a and 110b receiving the protruded electrodes 104a and 104b is used as shown in FIG. 50B, and the resin encapsulating operation is carried out while supporting the protruded electrodes 104a and 104b by this die 110.
However, the semiconductor chip 101 inclines in the molding resin 105 thus formed because the heights of protruded electrodes 104a and 104b from the pad electrodes 102 are different from each other. Therefore, a constant pitch may not be ensured between the protruded electrodes 104a and 104b on the surface of molding resin 105. More specifically, the protruded electrodes 104a and 104b are spaced out each other by a pitch L6 which is smaller than the proper pitch L5 between the protruded electrodes 104a and 104b as shown in FIG. 50A. This may result in difficulty in the operation mounting the plastic molded semiconductor package 100 on the printed board.
Further, due to the deviation in the exposed heights of the protruded electrodes 104 from the molding resin 105, the connection failure is liable to generate between the protruded electrodes 104 and the electrodes on the printed board.
In addition to the problems described above, a following problem may generate. Referring to FIG. 44, the protruded electrodes 104, which are used in the plastic molded semiconductor package 100 thus constructed, require a relatively large height. The protruded electrodes 104, however, are formed by the thick-film printing method or the like, so that it is difficult to form the high protruded electrodes 104 in view of productivity and other.
Therefore, the height of the protruded electrodes 104 cannot be increased sufficiently. Therefore, washing fluid cannot efficiently flows between the printed board and the plastic molded semiconductor package 100 mounted thereon in the washing step.
Further, the plastic molded semiconductor package 100 in the prior art is not provided with a heat radiator. Therefore, heat generated from the semiconductor chip 101 is liable to stay in the package.